Recently developed chemical vapor deposition processes have been remarkably successful at allowing engineers and scientists to coat delicate substrates and to form coatings and powders having improved performance characteristics for certain applications. The success of methods like CCVD has, in part, increased the interests and desires of engineers to find new techniques and processes that will allow the treating and coating of still other substrates and the development of coatings suitable for new applications.
The chemical vapor deposition processes that have been so successful include the combustion chemical vapor deposition (CCVD) processes described in U.S. Pat. Nos. 5,652,021; 5,858,465; and 5,863,604, and issued to Hunt et al. These patents, which are hereby incorporated by reference, disclose methods and apparatus for CCVD of films and coatings wherein a reagent and a carrier medium are mixed together to form a reagent mixture. The mixture is then ignited to create a flame or the mixture is fed to a plasma torch. The energy of the flame or torch vaporizes the reagent mixture and heats the substrate as well. These CCVD techniques have enabled a broad range of new applications and provided new types of coatings, with novel compositions and improved properties.
U.S. Pat. No. 5,021,401, which issued on Jun. 4, 1991 to Snyder et al., discloses a process for the fabrication of nickel-oxide insulation on a superconductor. The superconducting wire may be a niobium-tin superconductor. Purified carbonyl is contacted with non-reacted niobium and tin on the surface of the wire, thereby coating the wire with a nickel sub-oxide. Several different superconductors are disclosed as being coated with nickel-oxide to form an insulative outer layer. The thickness of the nickel-oxide coating is between 1.5 to 20 microns, and however, it is noted that this technique may not produce a sufficiently resistive layer for thicknesses below 1.5 microns.
An insulated wire is taught in U.S. Pat. No. 5,091,609, which issued on Feb. 25, 1992 to Sawada et al. The wire has a conductor core, an anodic oxide layer and an oxide insulating layer. The conductor is disclosed as either aluminum-clad copper wire or pure aluminum wire. Dipping the wire into sulfuric acid and then applying a positive voltage to the wire forms the anodic oxide film on the outer surface of the aluminum. The oxide layer is then deposited on the anodic oxide film using the sol-gel method. Typical values for the thickness of the anodic oxide film are given as 10 to 20 microns with the total thickness of the oxide layers being between 20 and 40 microns. While the oxide insulators in this reference provide good electrical insulation and strength, the thicknesses of these oxide coatings are much larger than the thicknesses required for certain applications.
U.S. Pat. No. 5,468,557, which issued on Nov. 21, 1995 to Nishio et al. is drawn to a ceramic insulated electrical conductor wire. The method of making the wire is also discussed. The wire has a conductor core of copper or a copper alloy and a stainless steel layer around the copper core. A chromium oxide film is formed on the stainless steel layer, and a outer ceramic insulator is formed on the chromium oxide layer. To form the stainless steel clad copper wire, the core is inserted lengthwise into a stainless steel pipe, and plastically working the wire to provide the desired size. The stainless steel has sufficient chromium such that when oxidized a chromium oxide film is formed on the outer surface. The outer ceramic insulator is then vapor deposited onto the chromium oxide film. While the chromium oxide film is from 10 nm to about one micron in thickness, the overall thickness of the insulating oxide is about 3-4 microns thick. The chromium film is provided to increase adhesion between the stainless steel and the outer ceramic layer. Thus, the methods described in this reference provide oxide coatings that are several microns thick and the reference fails to describe how such oxide coatings may be employed as an insulator.
In addition to the above described oxide insulators, other materials have been used to produce insulators on electrical conductors. A Japanese lacquer coating for a conductor is discussed in U.S. Pat. No. 5,767,450, which issued on Jun. 16, 1998 to Furuhata. The coated conductor is designed for use in extremely small coils such as those found in electrical watches. While the coatings taught in this reference are indeed thin (as little as 0.1 micron thick), the materials used to deposit these Japanese lacquer coatings tend to break down at raised temperatures. In addition, the production of these coatings is environmental unfriendly.
Another useful application of the deposition methods described in the prior art is to produce various coatings on polymer products. In particular, deposition techniques have been employed to produce barrier layers for polymer-based food and beverage packaging materials. The requirements of these packaging materials (besides delivering the product) include flexibility (or rigidity in some applications) and as a barrier to gas transport (oxygen, carbon dioxide, water vapor, etc.), aroma and flavor. While these polymer containers are somewhat protective, they are not impermeable due to their physical properties and inherent amorphous regions. These regions allow the transport of oxygen and water vapor, resulting in degradation of the food product contained therein. The rate of transport of oxygen and water vapor is dependent on both temperature and the thickness of the polymer packaging. Obviously, the thicker the packaging, the more costly to manufacture. Barrier layers of another material (such as silica) greatly reduce the permeability of the polymers on which they are coated, as well as increasing the scratch resistance or controlling the tribology of the outer surface of the packaging. The prior art methods of producing these barrier layers use vacuums, CVD and other complex or environmentally unsafe practices. Moreover, the adhesion levels between the polymer surface and the barrier layer have been low creating a risk of contamination as material may flake off the package and mix with the food or beverage.
U.S. Pat. No. 5,085,904, which issued on Feb. 4, 1992 to Deak et al. discloses barrier materials useful for packaging. A multi-layer structure is shown including a resin substrate, a layer of SiO vacuum deposited thereon, a layer of SiO2 vacuum deposited on the SiO layer and a protective outer layer of adherent plastic resin. The resin substrate may be a polyester resin or a polyamide resin. The silicon layers are all disclosed as being vacuum deposited and therefore the methods to form these coatings require vacuum equipment and have other disadvantages.
U.S. Pat. No. 5,683,534, which issued on Nov. 4, 1997 to Löfgren et al. and European Patent Specification EP 0 385 054 B1 published Sep. 5, 1990 both teach a method for the manufacture of laminated packaging material. The laminated material is a good gas and aroma barrier. The barrier layer is applied to the base layer using vacuum deposition, and includes an intermediate layer of bonding material. To aid in the package manufacturing, the barrier layer is omitted from areas that are intended to be folded.
A transparent high barrier multi-layer structure is described in U.S. Pat. No. 5,916,685, which issued on Jun. 29, 1999 to Frisk. In one embodiment of the structure, a layer of SiOx is deposited onto a polymer, x being between 1.5 and 2.5. The SiOx may be deposited using a number of different methods, although plasma-enhanced CVD is preferred. The polymer is selected from the group consisting of polyamides, polyethylene terephthalate, copolymers of polyethylene terephthalate and mixtures thereof. A clay mineral is integrated into the polymer. As with other prior art laminates, these products are produced using methods that have inherent disadvantages, including contamination due to poor adhesion and bonding.
None of the above references and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.